I've been looking at some birth records [atti di nascita] from the 1850's. In the annual index, both the father's and mother's names are normally listed. But in a few cases only the mother's name is listed, followed by the abbreviation "C.P.I."
Most of these births are to unwed mothers. In the birth record itself, "donna celibe" is appended to the mother's information, and the father's info is left blank. The child's surname is the same as the mother's, and he is not explicitly described as illegitimate, though it is obviously implied.
But in one case, the mother is described as "the legitmate wife of -----, who disappeared [scomparso] and has been absent [assente] from the town for two years." As in the case of the unwed mothers, the child has the mother's surname, and no father is given.
Can anybody tell me what C.P.I. stands for? It seems to refer to the mother, not the child, since it appears after the mother's name in the index. At first I thought it might refer to her marital status, but it is used for both single and married women. It might indicate that the mother is not married to the child's father, but that's just a guess.